New charges against Hoegel include 62 additional killings at Delmenhorst and 35 charges relating to the deaths at a facility in Oldenburg, where Hoegel worked from 1999 to 2002.
Hoegel was convicted in 2015 of two murders and two attempted murders in Delmenhorst and was given a life sentence.
Read on for more.
Hoegel killed his patients by administering overdoses of heart medication.
Now, Germany is coming to terms with the full scope of one of its most prolific serial killers since World War II - an apparent mass murderer who managed to escape suspicion for more than a decade because his victims were already critically sick in intensive care units.
The revelations date back to 2005, when a female nurse witnessed Hoegel trying to inject a patient at the Delmenhorst hospital. He later told investigators that he also killed patients in Oldenburg.
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An investigation into neglect at the hospital is ongoing. However, it is likely to challenge his likelihood of parole, which generally is considered after 15 years for prisoners serving a life sentence.
Speaking previous year, Oldenburg police chief Johann Kuehme said that he believes numerous killings could have been prevented had people been willing to speak out.
Detectives researching the case exhumed 134 bodies from 67 separate cemeteries and questioned the former nurse six times throughout the investigation.
Koziolek said that a "variety of drugs" were used in the killings.
When patients started suffering the effects of the drugs they were given, Hoegel is accused of failing to help them.
Police say the extent of the killings could have been prevented if local health officials had of alerted police straight away.
Criminal charges are also being brought against other former members of staff who worked at the clinics during the time.